replaced your master cylinder

[mlitz]

Who has replaced their brake master cylinder? I am no getting the peddle feel that I use to. If I double pump the brake peddle it will get stiffer and feel 100% better. I saw baddog's post for the brace and I think I am going to buy one of those also. If I do replace my master cylinder should i replace it with a stock legacy one? or are there better ones out there? do STI ones fit?

[StatGSR]

don't confuse brake feel with brake performance, if you have to double pump your brakes to get it hard, there is something wrong with your braking system (probably your MC). This cannot be fixed by a master cylinder brace, an MC Brace only prevents firewall deflection caused by pushing on the brake pedal, it cannot and will not improve the actual braking performance of your car, only your perception of your cars braking performance through pedal feel...

[Dead91silvia]

Miss read that at first...

Make sure the vacuum line from the booster to the intake is good... It's most likely a leak of air, or you might have a bad caliper or something...

Also try bleeding the brakes, you might have air in there... Just some ideas... I have never replaced a master in a Subaru that has been worn out yet... Just crash damaged...

[mlitz]

SI guess I forgot to add when my brake pedal felt the best was before one of my calipers froze. So I replaced all the calipers and now have front sloted rotors with hawk pads. So all brakes have bleed... I guess I could try to bleed my brakes again before replacing my master cylinder.
But if I do replace it is there a better option?

[elislider]

check with subaru to see if there is a recall for your master cylinder. there was for my 98 Legacy L wagon. the dealer replaced it for free (even with over 300k miles on the car)

if no luck there, then definitely re-bleed all your brakes. do them in order of what is furthest from the MC first (so, right rear, left rear, right front, left front, in that order)

[Wiscon_Mark]

I moved this to the appropriate tech section. I too, have never heard of a MC failure. There's an STi MC in the classifieds right now. It might be a bit of a DIY job, but it would definitely improve braking performance.

[elislider]

some MC swaps are easy upgrades, like the SVX MC swapped onto early imprezas. I don't know what is a good upgrade for the 2nd gen legacy.

[Baddog]

Id be curious about a mc swap too.

[jjay03]

I might replace my MC also if I dont get the brake feel I want after doing the rear brakes too.

[mlitz]

Okay so I am going to replace my master cylinder and I am going to use a late 97 to 04 legacy master cylinder. It has a smaller bore of 15/16 instead of 1 1/8, the way the lines go in to it is a litter different so I would like to see some pictures of how they route if someone could post some. When I do the swap I will post how I do it.

[96LegacyWagon]

Once again I come up with stuff like 'is it plugged in'... but:

1) Do you have enough fluid in the system?
2) Did you see any noticeable leaks from any of the lines?

[StatGSR]

whats your logic for changing to the smaller MC?

[mlitz]

Once again I come up with stuff like 'is it plugged in'... but:

1) Do you have enough fluid in the system?
2) Did you see any noticeable leaks from any of the lines?

yes every thing has checked out... it really feels like my peddle is getting softer and less responsive. the double pump on the brake peddle is not working as often and if I hit the brakes hard the peddle almost falls to the floor.

[mlitz]

whats your logic for changing to the smaller MC?

With a smaller bore size I will get more pressure.

[Garrison]

whats your logic for changing to the smaller MC?

With a smaller bore size I will get more pressure.
Reverse that. With a bigger piston you will get more pressure. A smaller piston will give you more "feel", which is what you don't want in this instance.

[mlitz]

http://www.automedia.com/Better_Brake_P ... 080501gh/1 (http://www.automedia.com/Better_Brake_Performance/pht20080501gh/1)

Brake line pressure is a different thing than the force you apply to the pedal. Force acts in one direction and is addressed in pounds. Pressure acts in all directions against surrounding surfaces and is addressed in pounds per square inch or PSI. "Levers" (brake pedals) can be used to change the force. Inside the hydraulic system, the surface area of the piston is what is affected by pressure. Decreasing the bore size of the master cylinder increases the pressure it can build. Pistons in master cylinders are specified by bore size. But there's a hitch: The area of a circle (or bore) is Pi–R-Squared. The area of the piston surface increases or decreases as the square of the bore size or diameter. For example, the area of a common 1-1/8-inch master cylinder is approximately 0.994-inch. The area of an equally common 1.00-inch bore master cylinder is approximately 0.785-inch. Switching from the larger master cylinder to the smaller version will increase the line pressure approximately 26.5% assuming that pedal ratio hasn't changed.

look at like me pushing on your skin with my finger and then pushing on your skin with a pencil point, I will get a good amount of pressure and more volume with my finger but with the pencil tip is a lot more pressure and less volume.

Also there has to be a reason Subaru went to the smaller bore size in late 97 to 04 right?

Any one have any pictures for me?

[Garrison]

Interesting. When I was more into bikes, I would routinely change the master cylinders on them to a smaller unit (19x18 vs 19x20) when I went to the track. The overall bite was lower, but the modulation was fantastic.

[mike-tracy]

Another thing you can do for pedal feel is swap in a single stage booster diaphram from a non abs early impreza.

[jjay03]

I just replaced my front brakes and the car stops alot better but the peddle still feels a bit mushy. I still think its my MC also.

[StatGSR]

You will also gain additional pedal travel with the smaller mc which may improve feel, but also means you might run out pedal, remember what you are using the mc for is to move the pistons in each of the calipers and the piston area on that end isnt changing. Keep in mind that your brake system can only take so much pressure before you into the abs or completly locked up, an decrease in mc size can make this happen with less force applied to the pedal.

[mlitz]

You will also gain additional pedal travel with the smaller mc which may improve feel, but also means you might run out pedal, remember what you are using the mc for is to move the pistons in each of the calipers and the piston area on that end isnt changing. Keep in mind that your brake system can only take so much pressure before you into the abs or completly locked up, an decrease in mc size can make this happen with less force applied to the pedal.

And that makes total since but I am not to worried about it as 97 (my year) through 02 use the same front and rear caliper.

[Alcology]

This might be a stupid question, but I didn't see it mentioned. Did you completely replace your brake fluid or just top it off after bleeding? I always replace my brake fluid completely. I bled my brakes once and it was squishy after as well so I did again and the squish went away.

[mlitz]

yup, bleed them 2 times.

still waiting on pictures...

[Caboobaroo]

How did you determined it is a bad master cylinder?

If I was checking for a nad master cylinder, I would start by by crimping off all 4 calipers. They sell correct brake line crimp tools at most auto parts places because if you use Vise Grips, it can damage the brake hoses. If the brake pedal still felt like crap, there are no external leaks and I'm 100% sure there was no air in the system, then I would replace the master cylinder.

[d1giPhux]

Id say its the brakes needing to be properly bled. If you don't see any leaks, then that's most likely the case. My 99 LGT 35th Anniversary had the master cylinder replaced under warantee.. but even at the time it was NOT necessary. I just got it done because it was free!

[mlitz]

Well I still have not replaced it yet... I am planing on doing a H6 rear upgrade and SS lines I got from Reasons group buy. If i am still having problems then I will look at getting a master cylinder.